Systems and methods for sensing vector selection in an implantable medical device

ABSTRACT

Methods and devices for sensing vector analysis in an implantable cardiac stimulus system. In an illustrative example, a first sensing vector is analyzed to determine whether it is suitable, within given threshold conditions, for use in cardiac event detection and analysis. If so, the first vector may be selected for detection and analysis. Otherwise, one or more additional vectors are analyzed. A detailed example illustrates methods for analyzing sensing vectors by the use of a scoring system. Devices adapted to perform these methods are also discussed, including implantable medical devices adapted to perform these methods, and systems comprising implantable medical devices and programmers adapted to communicate with implantable medical devices, the systems also being adapted to perform these methods. Another example includes a programmer configured to perform these methods including certain steps of directing operation of an associated implanted or implantable medical device.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/304,084, filed Jun. 13, 2014, now U.S. Pat. No. 9,364,677, which is acontinuation of U.S. application Ser. No. 11/441,522, filed May 26,2006, now U.S. Pat. No. 8,788,023. This application is related to U.S.application Ser. No. 11/441,516 filed on May 26, 2006, now issued asU.S. Pat. No. 7,623,909, and is titled IMPLANTABLE MEDICAL DEVICES ANDPROGRAMMERS ADAPTED FOR SENSING VECTOR SELECTION, and is related to U.S.application Ser. No. 11/442,228, filed on May 26, 2006 and titledIMPLANTABLE MEDICAL DEVICE SYSTEMS HAVING INITIALIZATION FUNCTIONS ANDMETHODS OF OPERATION.

FIELD

The present invention relates to the field of implantable medicaldevices. More specifically, the present invention relates to implantablemedical devices that detect cardiac activity.

BACKGROUND

Implantable cardiac stimulus devices often include circuitry fordetection of electrical cardiac activity to observe a patient's cardiacfunction. Methods of and devices adapted for identifying and/orselecting favorable sensing vectors are desired.

SUMMARY

The present invention, in a first illustrative embodiment, includes amethod of analyzing available sensing vectors to select a suitablesensing vector for use in cardiac event detection. The illustrativemethod attempts to select a sensing vector without a need for operatorinput by analyzing one or more sensing vectors to determine if asuitable sensing vector is available. If the analysis is inconclusive,the method may include requesting input from an operator to resolveapparent ambiguities in one or more sensed signals. Another illustrativeembodiment includes an implantable cardiac stimulus device adapted toperform the method of, or methods similar to, the first illustrativeembodiment. Yet another illustrative embodiment includes an externalprogrammer for use with an implantable cardiac stimulus device, whereinthe external programmer is adapted to perform the method of, or methodssimilar to, the first illustrative embodiment.

An illustrative embodiment also includes a method of sensing vectoranalysis in an implantable cardiac stimulus device that includesobserving whether a first vector is suitable, within a given set ofthreshold conditions, for cardiac event detection and, if so, selectingthe first vector for use in detection without considering additionalvectors. If not, one or more additional vectors may be analyzed as well.If none of the analyzed sensing vectors meet the threshold conditions,the best available vector may be selected.

Another illustrative embodiment includes a detailed method of analyzinga sensing vector. The detailed illustrative method may includecharacterizing detected events as QRS events, artifacts, orunidentifiable. If sufficient detected events are characterized as QRSevents, the sensing vector used to capture the detected events may beassessed for the quality of signal it receives. Otherwise, additionalanalysis of the unidentifiable events may seek to further categorizethese events to allow assessment of the quality of signal captured bythe sensing vector.

Yet another illustrative embodiment includes a method of cardiac signalanalysis in an implantable cardiac stimulus system having a plurality ofsensing electrodes and operational circuitry coupled thereto. Theillustrative method is performed by operational circuitry executingvectoring instructions relative to a first sensing vector. In theillustrative method, the vectoring instructions cause the operationalcircuitry to return one of: a score indicating the quality of a signalcaptured along the first sensing vector; at least two possible scoresindicating the quality of the signal captured along the first sensingvector wherein operator input is needed to determine which possiblescore is correct; or an indication that the sensing vector under reviewis unsuitable for cardiac signal sensing. The operational circuitry thendetermines whether the first sensing vector receives a score indicatingthat the first sensing vector is well suited to cardiac signaldetection, and if not, the operational circuitry executes the vectoringinstructions relative to a second sensing vector. Devices adapted forthese methods make up additional illustrative embodiments.

Another illustrative embodiment includes a method of cardiac signalanalysis in a programmer adapted for use in conjunction with animplantable cardiac stimulus device. The programmer may includeoperational circuitry for executing vectoring instructions relative to afirst sensing vector. In the illustrative method, the vectoringinstructions cause the operational circuitry to return one of: a scoreindicating the quality of a signal captured along the first sensingvector; at least two possible scores indicating the quality of thesignal captured along the first sensing vector wherein operator input isneeded to determine which possible score is correct; or an indicationthat the sensing vector under review is unsuitable for cardiac signalsensing. The programmer operational circuitry then determines whetherthe first sensing vector receives a score indicating that the firstsensing vector is well suited to cardiac signal detection, and if not,the programmer operational circuitry executes the vectoring instructionsrelative to a second sensing vector. Devices adapted for these methodsmake up additional illustrative embodiments.

Yet further illustrative embodiments make use of sensing vectorselection methods as described above, with first and second sensingvectors being identified as primary and secondary detection vectors oranalysis vectors. Devices, including at least implantable cardiacstimulus devices and/or programmers for use with implantable cardiacstimulus devices which are adapted for such methods, make up additionalillustrative embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1B, respectively, show subcutaneous and transvenous implantedcardiac stimulus systems relative to the heart;

FIG. 2 is a block diagram illustrating a method of initialization for animplantable cardiac stimulus system;

FIGS. 3A-3B are graphical representations of cardiac signalsillustrating an analytical form for identifying QRS and T-Waves;

FIG. 4 is a graph showing treatment of a cardiac signal for explanatorypurposes;

FIGS. 5A-5B illustrate a block diagram for a method of signal vectoranalysis;

FIG. 6 illustrates a simplified model of an illustrative method;

FIGS. 7A-7B illustrate a block diagram for a method of signal analysiswithin the vector analysis of FIGS. 5A-5B;

FIG. 8 illustrates a block diagram for a method of assessing cardiacsignal quality;

FIGS. 9A-9C illustrate a block diagram for a method of analyzing acardiac signal;

FIGS. 10A-10B illustrate a block diagram for a method of signal vectoranalysis;

FIG. 11 is a block diagram illustrating a method in which a primarysensing vector and a secondary sensing vector are selected for use indetecting and analyzing cardiac events; and

FIG. 12 is a block diagram for an illustrative embodiment.

DETAILED DESCRIPTION

The following detailed description should be read with reference to thedrawings. The drawings, which are not necessarily to scale, depictillustrative embodiments and are not intended to limit the scope of theinvention.

FIGS. 1A-1B, respectively, show subcutaneous and transvenous implantedcardiac stimulus systems relative to the heart. Referring to FIG. 1A,the patient's heart 10 is shown in relation to an implanted,subcutaneous cardiac stimulus system including a canister 12. A lead 14is secured to the canister and includes sensing electrode A 16, coilelectrode 18, and sensing electrode B 20. A can electrode 22 is shown onthe canister 12. Several vectors for sensing are therefore availableincluding A-can, B-can, and A-B. It should be noted that the use of thecoil electrode 18 as a sensing electrode is also possible. Illustrativesubcutaneous systems are shown in U.S. Pat. Nos. 6,647,292 and6,721,597, and the disclosures of these patents are incorporated hereinby reference. Some embodiments include a unitary system having two ormore electrodes on a housing as set forth in the '292 patent, ratherthan that which is shown. A unitary system including an additional leadmay also be used.

Referring now to FIG. 1B, a transvenous system is shown relative to apatient's heart 30. The transvenous cardiac stimulus system includes acanister 32 connected to a lead 34. The lead 34 enters the patient'sheart and includes electrodes A 36 and B 38. Additional electrodes forsensing or stimulus delivery may also be included, and also may be usedfor sensing in some embodiments of the present invention. In theillustrative example, electrode A 36 is located generally in thepatient's ventricle, and electrode B 38 is located generally in thepatient's atrium. The lead 34 may be anchored into the patient'smyocardium. Again, a can electrode 40 is shown on the canister 32. Withthis system, plural sensing vectors may be defined as well. In bothFIGS. 1A and 1B, one or more sensing electrodes may also be used forstimulus delivery. Some embodiments of the present invention may be usedin combination systems that may include sensing vectors defined betweentwo subcutaneous electrodes, a subcutaneous electrode and a transvenouselectrode, and two transvenous electrodes.

In the configurations of FIGS. 1A and 1B, there are multiple sensingvectors available. Detection of cardiac function along one of thesesensing vectors allows the implanted cardiac stimulus system todetermine whether treatment is indicated due to the detection andidentification of a malignant condition such as, for example, aventricular tachycardia. An implanting physician may perform vectorselection by directly diagnosing which of the captured vectors is best.However, this requires an assessment of cardiac function along severalvectors and may increase the time needed to perform implantation, andalso increases the risk of human error. Further, if the physician isneeded to perform vector selection, as patient physiology changes (whichmay happen if a fibroid develops around an implanted sensing electrode),the system is at risk of using a sub-optimal sensing vector until thepatient re-visits the physician. Finally, the selection of a vector hasoften been a task requiring specialized training, as selection of asuitable vector among those available is not necessarily intuitive.

A robust sensing vector selection method is desirable, as well asdevices adapted to perform such methods. The present invention, inillustrative embodiments, provides such methods and uses variouscriteria for doing so. Some embodiments include implantable devices andprogrammers for implantable devices that are adapted to perform suchmethods.

The systems shown in FIGS. 1A-1B may include operational circuitry and apower source housed within the respective canisters. The power sourcemay be, for example, a battery or bank of batteries. The operationalcircuitry may be configured to include such controllers,microcontrollers, logic devices, memory, and the like, as selected,needed, or desired for performing the illustrative methods set forthherein. The operational circuitry may (although not necessarily) furtherinclude a charging sub-circuit and a power storage sub-circuit (forexample, a bank of capacitors) for building up a stored voltage forcardiac stimulus taking the form of cardioversion and/or defibrillation.The operational circuitry may also be adapted to provide a pacingoutput. Both cardioversion/defibrillation and pacing sub-circuitry andcapacities may be incorporated into a single device. The methodsdiscussed below may be embodied in hardware within the operationalcircuitry and/or as instruction sets for operating the operationalcircuitry and/or in the form of machine-readable media (optical,electrical, magnetic, etc.) embodying such instructions and instructionsets.

Each of the devices 12, 32 may further include such components as wouldbe appropriate for communication (such as RF communication or inductivetelemetry) with an external device such as a programmer. To this end,programmers 24 (FIG. 1A) and 42 (FIG. 1B) are also shown. For example,during an implantation procedure, once the implantable device 12, 32 andleads (if included) are placed, the programmer 24, 42 may be used toactivate and/or direct and/or observe diagnostic or operational tests.After implantation, the programmer 24, 42 may be used to non-invasivelydetermine the status and history of the implanted device. The programmer24, 42 and the implanted devices 12, 32 are adapted for wirelesscommunication allowing interrogation of the implanted device(s). Theprogrammers 24, 42 in combination with the implanted devices 12, 32 mayalso allow annunciation of statistics, errors, history and potentialproblem to the user/physician.

In some embodiments, the following illustrative methods are performeddirectly by the implanted devices 12, 32 either independently(periodically or occasionally) or at the direction of a programmer 24,42. In other embodiments, the following methods are performed by usingthe implanted devices 12, 32 to perform data capture, with theprogrammer 24, 42 performing other analytical steps by downloadingcaptured data (for example, in real time, or in blocks of predeterminedsize). The programmer 24, 42 may prompt additional data capture assuitable for the illustrative methods below, and the programmer 24, 42may then direct the implanted devices 12, 32. Some methods may beperformed by distributing appropriate tasks between the implanteddevices 12, 32 and the programmer 24, 42.

FIG. 2 is a block diagram illustrating a method of detectioninitialization for an implantable cardiac stimulus system. For thevectoring method, a detection threshold for the implantable cardiacstimulus system is initialized by performing a process of detection withone or more available sensing vectors. For example, the method stepsshown in FIG. 2 may be performed for sensing vectors A-Can, B-Can, andA-B, shown in FIGS. 1A-1B. The steps may also be performed using vectorsincluding the shocking/coil electrode 18 shown in FIG. 1A as well as anystimulus electrodes in FIG. 1B, although the set under consideration isreduced for illustrative purposes in the following examples to A-Can,B-Can, and A-B.

A vectoring method is a method of analyzing one or more availablesensing vectors to select a sensing vector for use in detection. Themethod in FIG. 2 is used to set the sensing parameters for a vectoringmethod. FIG. 2 includes first setting an initial sensing floor, as shownat 50, preferably in a relatively low range (high sensitivity) so thatthe device will detect cardiac events that exceed the detection floor.For example, this initial sensing floor may be set to a percentage of ahistorical value measured over a number of previously detected cardiacevents, specific to the patient, a patient population, a particularimplantation configuration, or other suitable variables.

As shown at block 52, several iterations of a sub-method are performed.In block 52, an event is detected, as shown at 54, and the detectionfloor is then raised, as shown at 56. The event detection 54 may occurwhen the detection floor is crossed by the sensed signal, and mayinclude a refractory period during which detection is disabled.Iterations in block 52 may continue until a timeout occurs, as shown at58. The timeout 58 may occur, for example, when a 2-second period oftime expires without a detection occurring. The timeout may indicate thedetection floor has been raised above the received signal strength forcardiac events.

After the timeout at 58, the vectoring detection floor is set to apercentage of the detection floor that led to the timeout 58, as shownat 60. For example, the vectoring detection floor may be set to about40% of the level that led to the timeout. Next, time periods are set, asshown at 62, and vectoring analysis is performed as shown at 64. Thetime periods are explained by reference to FIGS. 3A-3B. The vectoringdetection floor may be set differently for each of the sensing vectorsbeing analyzed, since each vector may produce a different signalstrength than the other vectors. For example, the method shown in FIG. 2may be repeated for each of several vectors prior to performing anyvectoring analysis 64, or the method of FIG. 2 may be performed as apart of vectoring analysis for each individual vector.

FIG. 3A is a graphical representation of a cardiac signal illustratingan analytical form for identifying QRS and T-Waves. A cardiac signal isshown at 80. A vectoring detection threshold is shown at 82. An event isdetected at 84, when the cardiac signal 80 crosses the vectoringdetection threshold 82. A refractory period 86 occurs following thedetection 84. After the refractory period 86, a continuation time (CT)period occurs, as shown at 88. The peak occurring during the refractoryperiod 86 is at least initially assumed to be the R-wave, as shown at90. A peak signal value is identified during the CT period, as shown at92, and is assumed to be noise. This peak 92 may be the T-wave, but isnot necessarily so. In an illustrative example, the refractory period 86lasts 160 milliseconds, and the CT period 88 lasts 220 milliseconds,although these values may vary in other embodiments.

In the illustrative example, it is assumed (for vectoring purposes) thatthe longest QT interval will be about 400 milliseconds, and so the peakvalue detected during the CT period 88 is assumed to be the T-wave. Theillustrative method, with the parameters given above, is adapted for usewith a patient having a heart rate of 30-150 beats-per-minute (bpm). Thedetection threshold 82 is effective during the CT period 88, such that,if the sensed signal crosses the detection threshold 82 during the CTperiod 88, this will be treated as another detection.

FIG. 3B illustrates that a new detection 94 will be defined for athreshold crossing during the CT period 88A that follows a firstrefractory period 86A associated with a first detection 96. The newdetection 94 has its own refractory period 86B and CT period 88B. Givena rate of 150 bpm or less, the detections shown in FIG. 3B indicate adouble detection, as the detections are too close together. It can beseen that, when double detection occurs, sensing outside of the CTperiods 88A, 88B may not happen, although this is not always the case.As explained further below, the present methods are adapted to select atmost one of the detections 94, 96 as representative of a heart beat,while determining that the other detection 94, 96 is noise.

Because the different sensing vectors may detect events in differentforms, and because the targeted population for such devices often hasabnormal cardiac function, a prototypical PQRST form, as shown in FIG.3A, may not always occur. For example, the T-wave may be relativelylarger than the R-wave. Some of the present methods also include anability to set a flag that calls for an attending physician (the“operator) to observe the cardiac signal and determine whether theR-wave or T-wave has a greater amplitude. When certain conditions aremet, the flag is set and the operator may be asked for input.

FIG. 4 is a graph showing treatment of a cardiac signal for explanatorypurposes. During the vectoring example that follows, the capturedcardiac signal is marked to identify events. The signal, shown at 100,is detected relative to a detection threshold 102. When the signalexceeds the detection threshold, this is marked as an event. Thechronologically most recent event is marked event i, as shown at 106,while a contiguously prior event is marked i−1, as shown at 104. Theduration of time between detections 104 and 106, is defined asinterval_(i), while the height of peak 106 is amplitude_(i), and theheight of the noise peak following peak 106 is noise_(i). One goal is todefine the detected events and portions of the cardiac signal in amanner as shown in FIG. 4; the methods of FIGS. 5A-5B, as well as othermethods shown below, are adapted to achieve this goal, when possible.

FIGS. 5A-5B illustrate a block diagram for a method of sensing vectoranalysis. The illustrative method starts as 130. A first vector isanalyzed, as shown at 132. The details of analysis are further explainedelsewhere. This analysis may include performing the method of FIG. 2, orthe thresholds defined in FIG. 2 may be defined prior to performing themethod for the first vector or more vectors. The analysis may provide aScore, as shown at 136, or cannot provide a Score, and instead providesPossible Scores, as shown at 134.

The use of “Score” and “Possible Scores” terms should be explained. Inan illustrative example, the vectoring analysis observes parameters ofthe sensed cardiac signal to determine whether the signal is likelyuseful for cardiac event detection. In an illustrative example, intervalanalysis is used to determine whether “good” detections are occurring. A“good” detection may have a desirable range of signal-to-noise ratioand/or amplitude, and may avoid detecting undesired “events”(artifacts). If the interval analysis indicates regular detections areoccurring, and early detections are not occurring, a Score is calculatedfor the sensing vector. The Score is an example of a metric for thereceived signal that indicates the quality of the sensing vector forcardiac event detection purposes.

If the interval analysis does not, with certainty, parse out noisydetections from actual cardiac event detections, then two or morePossible Scores may be calculated, each based on an assumed resolutionof the ambiguity or uncertainty that prevents calculation of a scorewithout ambiguity. For example, two Possible Scores may be calculated,one assuming the QRS peak exceeds the T-wave or other noise peak, andthe other assuming the QRS peak does not exceed the T-wave or othernoise peak. The following illustrative examples utilize a particularcalculation of Scores and Possible Scores for sensing vectors, thedetails of which may be modified in various suitable ways. It issufficient that the Score or other metric provide an indication of thequality of the signal captured along a sensing vector for purposes ofcardiac event detection and/or analysis.

Returning to the example in FIG. 5A, if the analysis yields onlyPossible Scores, as indicated at 134, a question flag is set for thefirst vector, as shown at 138. The question flag indicates that theoperator may need to provide input to the vectoring process to determinewhich of the Possible Scores is the correct Score to use for the firstvector by observing whether “QRS>T-wave?”. However, rather thanimmediately asking the operator's assistance, the method insteadanalyzes the second vector, as shown at 140.

Returning to step 136, if a score is provided for the first vector, themethod next determines whether the score for the first vector exceeds apredetermined threshold, as shown at 142. In the illustrative method, ifthe threshold is exceeded, this indicates that the first vector providesexcellent sensing, and further analysis is deemed unnecessary.Therefore, if the threshold is exceeded for the first vector, the methodends by selecting the first vector, as indicated at 144. Otherwise, themethod goes on to analyze the second vector, as shown at 140. Thus, themethod tests sensing vectors in a preferential order with vectors thatare less likely to yield high-quality results being tested after other,often more favorable vectors have been tested.

As with the first vector, analysis of the second vector either yields aScore, as indicated at 152, or cannot yield a score and instead providesPossible Scores, as shown at 150. If Possible Scores are provided, thequestion flag is set for the second vector, as shown at 154. The methodthen goes to A, as shown at 156, which continues in FIG. 5B.

If, instead, analysis of the second vector yields a Score, the methodcontinues from block 152 to determine whether the Score for the secondvector exceeds a threshold, as shown at 158. Again, if the threshold isexceeded, this indicates the second vector provides excellent sensingand so the method ends by selecting the second vector, as shown at 160.Otherwise, the method continues to A 156 in FIG. 5B. The steps shown forthe first and second vectors may be repeated for any number of vectors,depending upon the particulars of the implantable cardiac stimulussystem.

Referring to FIG. 5B, from A 156, the method determines whether any ofthe question flags have been set, as shown at 162. If not, the methodsimply selects the sensing vector with the best Score, as shown at 164.If one or more flags have been set, the method continues at 168 byanalyzing the Possible Scores. The operator (the attending physician)may be asked questions regarding any of the relevant Scores or PossibleScores.

The analysis at 168 may include determining whether any questions needto be asked. For example, if at least one vector yields a Score, andnone of the available Possible Scores from other vectors exceed thehighest Score, the operator is not asked any question, since thePossible Scores cannot provide the best available vector. Further, theoperator may be asked only relevant questions by selecting the vectorhaving the best Possible Score first. The operator is asked thequestion(s), as shown at 170. If the operator answer eliminates the bestPossible Score, the method may iterate to ask additional questionsrelative to one or more next-best Possible Scores. Or, if the answereliminates the best Possible Score, and the remaining highest score is aScore, rather than a Possible Score, a corresponding sensing vector isselected. Then, the sensing vector with the best Score is selected, asshown at 164.

It should be noted with respect to FIGS. 5A-5B that the portion of themethod shown in FIG. 5A selects a vector depending on whether the vectorprovides a sufficient Score. The portion of the method in FIG. 5B, onthe other hand, selects the vector with the best Score.

In some embodiments, both first and second sensing vectors are selected,with the first sensing vector being a primary or default sensing vectorand the second sensing vector being an alternative or clarifying vector.For example, during a given cardiac episode, if the first vectorprovides at best ambiguous indications of whether therapy is needed, thesecond vector may be used to resolve any ambiguity. In otherembodiments, a second sensing vector may be identified during theinitialization procedure in case, at a later time, the first sensingvector becomes unsuitable (due to changes in physiology, external noise,etc.) or unavailable (due to mechanical failure, for example). Forembodiments identifying first and second sensing vectors, the method ofFIGS. 5A-5B may simply continue, using similar steps and processes,until a second vector is identified in like fashion.

An illustrative method is shown by FIG. 6. A sensed signal is parsedusing detection techniques into various significant features including,for example, peak amplitudes, intervals between peaks, and noise levelsbetween peaks. FIG. 5 illustrates an analytical form for this firststep. Next, the features identified by the detection techniques arefurther analyzed to reduce the number of variables under consideration.In the illustrative example of FIG. 6, a set of {n} detected events isanalyzed to generate a set of {a} identified QRS peaks and associatednoise levels, where the only known relationship between n and a is thatn>a. Because the sensed signal may not readily parse and condense intothe data pairs shown, allowance is made for ambiguity during signalprocessing by carrying forward “additional data” as well. If necessary,the implications of the “additional data” may be determined by seekinguser input, as further set forth below.

FIGS. 7A-7B illustrate a block diagram for a particular form of themethod of FIG. 6. The method illustrated in FIGS. 7A-7B is a particularform for transferring data related to a sensing vector into metrics forevaluating the merits of a given sensing vector against one or morethresholds and/or other sensing vectors. From start block 200, themethod identifies a detection threshold for vectoring, as shown at 202.In some embodiments, step 202 may be achieved by the method of FIG. 2,for example. Next, the illustrative method captures {n} contiguousdetected events, as indicated at 204. The “detected events” may occurwhen the detection threshold is crossed by the sensed signal. Selecteddata samples associated with the detected events are also kept foranalysis. In an illustrative embodiment, n=11, although other larger orsmaller sets of events may also be used. An iterative analysis followsfor events marked initially with the i variable, with the iterativemethod continued until i>=n, although in some embodiments the method mayabort if it becomes clear that the vector being considered isunsuitable. For the first iteration, coming from block 204, the methoduses i=1 and also sets another variable a=1.

The loop then starts for the {n} detected events by considering theinterval between a first (i−1) event and a second (i) event. As shown at206, an interval between the i^(th) event and the i−1^(th) event,Interval(i), is compared to a threshold, with 400 milliseconds used forillustrative purposes. If the threshold is not exceeded, the methodcontinues at B, as shown at 210, in FIG. 7B, unless, as indicated atstep 208, the first interval was being considered (Interval(1), in whichcase the method simply iterates to i=2, as shown at 212, and loops backto step 206 again. If, at 206, the interval is greater than thethreshold, then the interval is stored as Interval(a), as shown at 214,and the peak captured during the i^(th) refractory period is stored asQRS(a), as shown at 216.

The interval between i and i+1 (Interval(i+1)) is then considered asshown at 218, and compared to a threshold, which is again shown forillustrative purposes, as 400 milliseconds. If, at 218, the threshold isexceeded, then the peak signal captured during CT(i), the continuationtime that follows refractory for the i^(th) detection, is stored asNoise(a), as indicated at 220. The method then iterates as shown at 222,and returns to step 206 but with i=i+1 and a=a+1.

Returning to step 218, if the (i+1)^(th) interval considered there doesnot exceed the threshold, then the refractory peak that caused thelatter detection is stored as Noise(a), as shown at 224. This occursbecause it is assumed that the latter detection occurred too close tothe prior detection to be another QRS complex. The illustrative400-millisecond threshold interval is used in association with a methodthat should be performed when the patient's heart rate is in the rangeof about 30 to 150 beats-per-minute (bpm). Detections occurring withless than a 400-millisecond interval would correspond to a higher beatrate (150 bpm or more), and therefore the method assumes that shorterintervals indicate one or more detections are caused by noise. Themethods may be tailored to other patient beat rates, if desired.

From 224, the next iteration starts at 226 after another iteration, thistime with i=i+2 and a=a+1. The i variable receives a double iterationsince, as shown at 224, the (i+1)^(th) peak is considered to be noise.When returning to step 206, in some embodiments the next interval istaken from i−2 to i, spanning the i−1 event that has been identified aslikely occurring due to noise. For example, at a microcontroller level,a flag may be set to indicate double iteration at step 226, the flagbeing reset once the interval is considered in step 206.

Turning now to FIG. 7B, the method picks up at block B 210, whichcontinues from block B 210 in FIG. 7A. As shown at 232, the methodcontinues by determining whether a “Long QT” condition has been checked.In an illustrative embodiment, the “Long QT” condition allows anoperator to indicate to the implantable device system and/or theprogrammer that the patient is susceptible to a long interval betweenthe Q and T signals. For such a patient, the T-wave is likely to occurrather late after the R-wave in the overall cardiac cycle. By referenceto the analysis using a refractory period and CT interval, as shown inFIG. 3A-3B, a “Long QT” patient may experience the T-wave afterexpiration of the CT interval. This may cause the detection circuitry todetect a threshold crossing due to the T-wave artifact after the CT timeperiod expires in one or more sensing vectors.

If the “Long QT” condition is checked, the method continues withamplitude analysis, as indicated at 234. An illustrative method ofamplitude analysis 234 is further explained below by reference to FIGS.8 and 9A-9C. After amplitude analysis at 234, the method iterates usingi=i+1, and returns to block C 228 in FIG. 7A, which ultimately sendsanalysis to block 206. It should be noted that the {a} variable is notiterated here, as the data elements QRS(a) and Noise(a) have not beenfilled with data during amplitude analysis at 234.

If the “Long QT” condition is not checked at block 232, the methoddetermines whether Interval(i−1) and Interval(i) are very similar inlength. In an illustrative example, the intervals are considered to bevery similar in length when their durations are within 50 millisecondsof one another, for example, 300 milliseconds is considered very similarin length to 320 milliseconds, although the exact parameters fordetermining similarity may vary. If the intervals are very similar inlength at 238, the method continues with amplitude analysis, as shown at234, as before.

If the intervals compared at 238 are not similar, the method determineswhether Interval(i) is longer than Interval(i−1), as shown at 240. Ifso, then Peak(i) is stored as QRS(a), as shown at 242. Otherwise, ifInterval(i−1) is not shorter than Interval(i), the method decrements the{i} variable to i=i−1, as indicated at 244, and continues to step 242.Using either course, the method continues from step 242 to D, as shownat 230, which returns to FIG. 7A, directing the method to step 218.

Detected events that are analyzed in FIGS. 7A-7B and found to be QRSevents are placed in a QRS bin, while events that are found to be noiseare placed in a Noise bin. Those events that undergo amplitude analysisare placed in bins as illustrated in FIG. 8. In some embodiments, themethod may be aborted if too many events are placed in bins foramplitude analysis, although this is not necessarily the case.

FIG. 8 illustrates a block diagram for a method of assessing cardiacsignal quality. This method may be a part of the amplitude analysis 234shown in FIG. 7B. From start block 250, the method receives a pair ofevents a and b, as shown at 252. Event b is to be placed in one ofseveral bins, as indicated at 254, depending upon the relativeamplitudes of events a and b. More particularly, if the amplitudes ofpeaks a and b are more or less equal, within +/−15% margin, event b isplaced in the EQUAL bin, as shown at 260, 262. If peak b is larger thanpeak a, outside of the margin for the two being equal, then b is placedin the HIGH bin, as shown at 256, 258. Conversely, if peak a is muchgreater than peak b, then b is placed in the LOW bin, as shown at 264,266. The binning process of FIG. 8 is used later in FIGS. 9A-9C.

FIGS. 9A-9C illustrate a block diagram for a method of analyzing acardiac signal. The method of FIGS. 9A-9C is a method for calculating aScore for a given vector. The method assumes the use of the methods ofFIGS. 7A-7B to analyze {n} contiguous detected events. These events, asexplained above, may generate paired Noise and QRS data elements, whichare separated and placed in a QRS bin and a NOISE bin. Also, with theamplitude analysis of FIG. 8, some events related to ambiguous intervalsmay be placed in bins for HIGH, LOW and EQUAL.

For illustrative purposes, the example of FIGS. 9A-9C uses n=11 as thenumber of initially detected events. In other embodiments, any suitablenumber of events may be used. The parameters used in the followingexample are merely illustrative of one manner of performing the method,and may be modified to suit other systems, specific circumstances, orvariables. The method of FIGS. 9A-9C begins at a start block, anddetermines whether 6 or more of the n=11 detections have been placedinto the QRS bins, as shown at 300. If not, the method continues withblock X 304 in FIG. 9B.

If there are 6 or more detections in the QRS bin, then the averageamplitudes for noise and QRS bins are calculated, as shown at 304. Anillustrative method of performing this calculation is shown in block306. The standard deviation is determined for the noise data, as well asthe mean. Then the average is calculated by excluding any outlying data(illustratively, data that falls outside of one standard deviation ofthe mean). The process is repeated for the QRS data as well.Alternatively, the method shown in block 312 may be used instead tocalculate averages for one or both of Noise and QRS data. In thissomewhat simpler method, a highest data point and/or a lowest data pointare removed from the data set and the average is calculated using thereduced data set, as shown at 312.

The SNR is then calculated as the ratio of the average amplitude of theremaining events in the QRS bin to the average of the amplitudes storedin the NOISE bin, as shown at 308. Next, the SCORE is calculated usingthe average amplitude of the remaining events in the QRS bin along withthe SNR, as shown at 310. In an illustrative example, the followinglookup table is used to find the SCORE:

LOOKUP TABLE Amplitude Range S_(A) (mV) S_(R) SNR 0.5 ≤0.5 0.5 ≤3 5 0.5-0.65 1 3-3.5 10 0.65-0.8  25 3.5-4   18 0.8-1.0 50 4-5   30 1.0-1.775 5-7.5 20 1.7-2.0 100 >7.5 40 2.0-3.0 15 3.0-3.5 0.5 3.5-4.0The illustrative lookup table is adapted for a system in which thedevice is adapted to sense with either a LOW or HIGH amplitude input,having dynamic ranges of either ±2.0 millivolts or ±4.0 millivolts. Forthis illustrative system, peak amplitudes in the 1.7-2.0 millivolt rangecreate a likelihood of clipping and/or difficulty in using only one ofthe two dynamic ranges all the time. Likewise, peak amplitudes in therange of 3.5-4.0 millivolts create a likelihood of clipping as well,making this a less preferred range such that a lower SA factor isprovided. The lookup table may be adapted for other systems havingdifferent characteristics.

In some embodiments, the dynamic range of the analysis system for use inassociation with the vector under consideration may be set dependingupon the average value found and/or the mean of the QRS data. Forexample, the method may include selecting a dynamic range for theanalog-to-digital converter, incoming signal amplifier, or othercomponent(s) of the system.

Next, the Score is determined from:S _(A) *S _(R)=ScoreWith the score calculated at 310, scoring is complete, and the methodends.

In an illustrative embodiment, the above scoring chart is used inassociation with the method of FIGS. 5A-5B with the thresholds forselecting one of the first or second sensing vectors being set at 1750.For example, a calculated amplitude of 2.2 volts, with an SNR of 4.5,would score 2000, sufficient to have a sensing vector automaticallyselected without further consideration of other vectors. Theseparameters may be adjusted in light of system capabilities and/orrequirements. In other embodiments, rather than a scoring chart, aformula may be used.

Turning now to FIG. 9B, the method picks up at block X 302, coming fromFIG. 9A. The method determines whether there are 6 or more (again, outof 11, although these numbers may be varied) detections in the EQUALbin, as indicated at 320. If so, the sensing vector under considerationis yielding too many ambiguous results and too much noise, causingoverdetection that the system has a difficult time resolving. Therefore,the sensing vector is declared bad, as shown at 322, and the scoringmethod ends as no Score can be returned for the vector underconsideration. The overall vectoring method would, at this point,continue analysis with a different sensing vector.

If the condition at 320 is not true, then it is determined whether thereare at least 3 of 11 detections in the QRS bin, as indicated at 324. Ifnot, the method continues at block Y 326 and on to FIG. 9C. If there are3 or more detections in the QRS bin, the method continues at 328, theAverage for NOISE and QRS are each calculated. This may be performed inaccordance with one of the methods of blocks 306 or 312 of FIG. 9A,although, due to the reduced data set initially under consideration, themethod of block 312 may be more useful, as the statistical analysis ofblock 306 is less useful.

Next, the QRS Average and NOISE Average are compared to one another toverify that the bins contain values that are separated from one another,as shown at 330. The use of 1.15 as a multiplier is merely illustrativeof one form of this comparison. In another embodiment, rather than amultiplier, an offset having a stable value is used, or a formula suchas Ax+B may be used, with A as a multiplier and B as an offset. Othercomparisons may also be made to determine separation. If the values inthe QRS and NOISE bins are too close to one another, the method jumps tostep 334, where a bad vector is declared and scoring ends.

If the condition at 330 is met, the remaining values in the EQUAL, HIGHand LOW bins are analyzed to see which, if any, can be moved to one ofthe QRS or NOISE bins, as indicated at 332. The data points in theEQUAL, HIGH and LOW bins are moved to QRS and/or NOISE by the methodsteps shown in block 336. For each data point, j, the peak amplitude iscompared to see if it may fit in one or the other of the QRS or NOISEbins due to its amplitude similarity, using a +/−15% margin to determinesimilarity. If the data point, j, is sufficiently similar to the averageof either the QRS or NOISE bin, it is then moved to that bin. Steps thatmove j to the QRS bin are shown at 338, 340, and steps that move j tothe NOISE bin are shown at 342, 344.

After each data point in the EQUAL, HIGH and LOW bins has beenconsidered in block 336, it is again determined whether there are 6 ormore detections in the QRS bin, as indicated at 346. Next, the Averagesfor the NOISE and QRS bins are recalculated, as indicated at 350, forexample, by the method of one of blocks 306 or 312 in FIG. 9A. Next, theSNR is determined as shown at 352, and a score is calculated as shown at354. Once the Score is found at 354, the scoring method ends, as notedat 356.

If the condition at 346 fails, and there are still less than 6detections in the QRS bin after block 338, the QRS, NOISE, HIGH, EQUALand LOW bins may be reset to their original status prior to steps336-344, as shown at 348. The method then goes to block Y 326, andcontinues in FIG. 9C.

Turning to FIG. 9C, the method continues from block Y 326. It isdetermined whether there are 2 or more detections in the HIGH bin, asindicated at 360. If not, then a bad vector is declared, as indicated at362, and the scoring method ends because a score cannot be returned forthe vector under consideration.

If there are at least 2 detections in the HIGH bin, the method goes fromblock 360 to 364, where the average amplitudes for the data points inthe HIGH and LOW bins are computed. This may be performed using a methodsimilar to those shown in one of blocks 306 or 312 in FIG. 9A or,instead, because the data set under consideration is already limited,the full set of data points in each bin may be used to calculateaverages in step 364.

The next step is to attempt to move points from the EQUAL bin into theHIGH and LOW bins, as shown at 366. This is performed as indicated inblock 368. For each data point k in the EQUAL bin, the amplitude storedfor that data point is compared to the average for the HIGH bin, asshown at 370, to determine if it is similar to the average for the highbin, within a defined margin of +/−15%. If so, then the data point k ismoved to the HIGH bin, as shown at 372. Otherwise, the amplitude for kis compared to the average for the LOW bin, again with a margin of+/−15%, as shown at 374. If the amplitudes are similar, k is moved tothe LOW bin, as indicated at 376. These steps are repeated for eachpoint k in the EQUAL bin.

After block 368 is completed, the method determines whether 4 or moredetections are in the HIGH bin, as indicated at 380. If not, then a badvector is declared as shown at 382, because no score can be returned. Ifthere are 4 or more points in the HIGH bin, then possible scores aredetermined, as indicated by 384.

As shown in block 386, a TWave_Larger Score is calculated. This PossibleScore assumes that the T-wave will have a greater amplitude than the QRSsignal. Therefore, it assumes that the detections in the HIGH binrepresent T-waves, while the detections in the LOW bin represent QRSsignals. Therefore the SNR is calculated as the ratio of the averageamplitude in the LOW bin to the average amplitude for the HIGH bin. Thismay be performed using the full data sets in each of the LOW bin andHIGH bin, or the data sets may be reduced by methods such as shown inblocks 306 and 312 in FIG. 9A. The variable “Amplitude” is then set asthe average amplitude for the LOW bin (again, a full or reduced data setmay be used to calculate the average amplitude for the LOW bin) as well.The Possible Score is determined as before by the use of the look-uptable or chart, although again, other methods could also be used.

Next, as shown at 388, a QRS_Larger Score is calculated. This PossibleScore assumes that the QRS signal will have a greater amplitude than theT-wave. Therefore, it assumes that the detections in the HIGH binrepresent QRS signals, and the detections in the LOW bin representT-waves. The SNR is calculated as the ratio of the average amplitude inthe HIGH bin to the average amplitude in the LOW bin in similar fashionto that used in block 386, and the amplitude is calculated as theaverage amplitude for the HIGH bin, again using either full or reduceddata sets. The Possible Score is then calculated as before.

After the creation of the Possible Scores (QRS_Larger SCORE andTWave_Larger Score) in steps 386, 388, a flag is set for asking theoperator whether “QRS>TWave?” as indicated at 390. If necessary, i.e. ifthe largest available score is one of the possible scores, the operatorcan then provide an input that indicates which of the possible scores iscorrect. With the flag set at 390, the Scoring method ends as indicatedat 392 by returning the two possible scores with the flag set.

FIGS. 10A-10B illustrate a block diagram for a method of signal vectoranalysis. The method assumes a system as illustrated in one of FIGS.1A-1B, with three sensing vectors available: A-Can, B-Can, and A-B. Theillustrative vectoring method of FIGS. 10A-10B displays a preference forthe A-Can vector, then the B-Can vector, and a lowest preference for theA-B vector. This is not necessary to the practice of the invention, butFIGS. 10A-10B illustrate how such preferences can be incorporated into avectoring method.

The method begins at block 400, where the sensing vector A-Can isanalyzed. As shown at 402, the first query is whether a Score(A) (aScore for the A-can sensing vector) has been calculated during theanalysis 400. If so, the method continues at 404 where the generatedScore(A) is compared to Level(A), a threshold for the A-Can sensingvector. If Score(A) exceeds Level(A), then the method selects the A-Cansensing vector, as indicated at 406, which ends the vectoring method ifonly one sensing vector is sought. If multiple sensing vectors aresought, then the method may continue by analyzing the other availablevectors to select a secondary vector, if desired.

If Score(A) does not exceed Level(A), then the method goes to block 408,where the B-Can sensing vector is analyzed. Going back to block 402, ifa Score cannot be calculated for the A-Can sensing vector, it isdetermined at 410 whether the A-Can sensing vector is a bad vector, asindicated at 410. If so, the A-Can sensing vector may be marked as bad,and the method jumps ahead to step 408. Otherwise, the method continuesto block 412, where the flag for indicating that operator input isneeded relative to the A-Can sensing vector is set. With analysis of theA-Can sensing vector complete, the method continues to block 408 wherethe B-can sensing vector is analyzed.

From block 408, it is again determined whether a Score(B) (a Score forthe B-Can sensing vector) has been calculated, as shown at 420. If so,the method determines whether the Score(B) is greater than Level(B), athreshold for the B-Can sensing vector, as shown at 422. As before, ifLevel(B) is exceeded, the B-Can sensing vector is determined to besufficient for detection use and the method ends (if only one sensingvector is sought) by selecting the B-Can sensing vector, as indicated at424. If Level(B) is not exceeded, the method continues to step 426,further explained below.

If no Score(B) is calculated, the method determines whether the B-Cansensing vector is a bad vector, as indicated at 428. If so, the B-Cansensing vector may be marked as bad, and the method again continues atstep 426. If the B-Can sensing vector is not a bad vector at 428, themethod sets a flag indicating that operator input is needed to finishanalysis of the B-Can vector to generate a Score, as indicated at 430.Again, the method continues to step 426.

At step 426, it is determined whether Score(A) exceeds Score(B). If aScore for either A-Can or B-Can could not be calculated, then step 426will determine that whichever Score was calculated is greater. Ifneither Score was calculated, then the method goes directly to block Z442 since the comparison is not applicable. If Score(A) is greater, thenthe method compares Score(A) to Level(X), a second threshold for theA-Can sensing vector, which may be lower than the threshold set byLevel(A). If the second threshold is exceeded, the method selects A-Can,as shown at 436. Otherwise, the method goes to block Z 442. If Score(B)is greater, then the method compares Score(B) to Level(Y), a secondthreshold for the B-Can sensing vector, which may, again, be lower thanthe threshold set by Level(B). If Level(Y) is exceeded, the methodselects the B-Can sensing vector, as indicated at 440. Otherwise, themethod continues to block Z 442, which goes to FIG. 10B.

If desired, the thresholds Level(A) and Level(B) may be set at the samelevel. Likewise, the thresholds Level(X) and Level(Y) may also be set tothe same level. In other embodiments, a factor may be included in thecomparison at 426 to favor one or the other sensing vector. In anotherillustrative embodiment, the above look-up chart for finding factors SAand SR is used, with these factors next being multiplied to yield aScore. For the illustrative example, Level(A)=Level(B)=1750, andLevel(X)=Level(Y)=750.

Referring now to FIG. 10B, the method continues from block Z 442 withthe analysis of the A-B sensing vector, as indicated at 450. It is thendetermined whether a Score(AB) (the Score for sensing vector A-B) can becalculated, as indicated at 452. If so, then it is determined whetherScore(AB) is greater than Level(AB), a threshold defined for the A-Bsensing vector, as shown at 454. If so, then the A-B sensing vector isselected, as shown at 456. In an illustrative embodiment, Level(AB)=750,using the look-up chart to find SA and SR, and comparing the product ofSA and SR to Level(AB). If Level(AB) is not exceeded, the method goes tostep 458, which is further explained below.

If Score(AB) cannot be calculated at step 452, the method continues tostep 460, where it is determined whether the A-B sensing vector is a badvector. If so, the A-B sensing vector may be marked as a bad vector andthe method continues to 458. If the A-B sensing vector is not a badvector, the method continues to step 462 and sets the flag to indicatethat operator input is needed to resolve an ambiguity with the A-Bsensing vector. The method then continues to step 458, as explainedbelow.

Step 458 indicates the observation of Available Scores. The AvailableScores include calculated Scores and calculated Possible Scores. Block468 indicates the characterizations that may occur. For each vectorA-Can, B-Can, and A-B, there are three outcomes for the precedingillustrative example: a Score, a pair of Possible Scores, or a BadVector mark. As such there are 27 possible combinations, from 3 scoresto 3 possible scores to 3 bad vectors, with a maximum of 6 AvailableScores (2 Possible Scores for each sensing vector).

From the Available Scores, a largest score or possible score (LSPS) isidentified, as shown at 470. Next, it is determined whether the LSPS isa Score, as indicated at 472. If so, then the sensing vectorcorresponding to the LSPS is selected, as shown at 474, and the methodis over. If the LSPS is not a Score, then the operator is asked whetherQRS>T for the sensing vector that corresponds to the LSPS, as indicatedat 476. The answer given by the operator can either verify or reject theLSPS, depending upon whether the calculation resulting in the LSPScorresponds to the answer given by the operator.

For example, if the LSPS is the QRS_Larger Score for the A-Can sensingvector, the operator will be asked whether, for the A-Can sensingvector, QRS>Twave? If the operator indicates “Yes”, then the operator'sanswer verifies the QRS_Larger Score for the A-Can sensing vector, andtherefore the LSPS would be verified. If, instead, the operator's answeris No, then the TWave_Larger Score for the A-Can sensing vector would beverified, and the QRS_Larger Score would be discarded because theoperator's answer indicates it is an incorrect calculation.

As indicated at 478, the method next determines whether the LSPS isverified by the operator's response to the question at 476. If so, thenthe sensing vector corresponding to the LSPS is selected, as indicatedat 474. Otherwise, the LSPS is discarded, as indicated at 480, and themethod returns to step 470, but this time with a Score for the LSPSsensing vector from the last iteration, rather than two Possible Scores.

FIG. 11 is a block diagram illustrating a method in which a primarysensing vector and a secondary sensing vector are selected for use indetecting and analyzing cardiac events. As shown at 500, the methodfirst identifies a primary sensing vector. This may be performed, forexample, using the methods discussed above.

Next, the method includes identifying a secondary sensing vector, asshown at 502. This may be performed in more than one fashion. Forexample, as shown at 504, the method used to find the primary sensingvector may be repeated in its entirety, with the method ending at 506.In another embodiment, the method simply continues analysis afteridentifying the primary sensing vector. As shown at 510, if all of theavailable sensing vectors have already been analyzed, the method picksthe best one and, again, ends at 506.

If not all vectors have been analyzed, then an additional vector isanalyzed as shown at 512. If this additional vector meets a firstthreshold at step 514, illustrating that the additional vector is wellsuited to cardiac signal analysis, then the additional vector isselected as the secondary vector, and the method ends at 506. In anotherembodiment, a flag is set if not all vectors have been analyzed at 510,and an additional step is performed at the end of the method to comparethe score for the primary vector to the score for the secondary vector.If the secondary vector has a higher score than the primary vector,their designations may be reversed.

If the additional vector does not meet the first threshold at step 514,the method loops back to step 510. The loop continues until either anewly analyzed vector exceeds the threshold at step 514, or all vectorshave been analyzed and the best one is selected at step 510. The use ofprimary and secondary vectors may take several forms, such as thosediscussed in co-pending U.S. application Ser. No. 10/901,258, filed Jul.27, 2004, now U.S. Pat. No. 7,392,085 and titled MULTIPLE ELECTRODEVECTORS FOR IMPLANTABLE CARDIAC TREATMENT DEVICES, the disclosure ofwhich is incorporated herein by reference.

FIG. 12 is a block diagram for an illustrative embodiment. Theembodiment of FIG. 12 illustrates a generic method. Beginning at block550, the method includes selecting a detection threshold. Next, a set ofevents is captured, as indicated at 552, using the detection thresholdto define cardiac events sensed along a selected sensing vector. The setof events is analyzed as shown at 554. The analysis at 554 results in adetermination at 556. The sensing vector used to capture the set ofevents at 552 is determined at step 556 to be one of a suitable vector,an available vector, or an unsuitable vector, as shown at 558, 562, and570, respectively.

If the sensing vector is determined to be a suitable vector as shown at558, then the sensing vector has been found to have met selectedparameters for finding a suitable cardiac sensing vector. A vectormeeting the selected parameters is, in the illustrative method, assumedto be likely sufficient to provide accurate cardiac monitoring.Therefore, in the illustrative method, further consideration ofadditional sensing vectors is considered unnecessary. Therefore, asindicated at 560, the method ends without further analysis of additionalsensing vectors. The suitable vector is then used for cardiac eventdetection and analysis.

If, instead, the sensing vector is determined to be an available vector,as shown at 562, then the vector under consideration is considered acandidate for data capture, but does not meet the parameters to renderfurther consideration of additional sensing vectors unnecessary. Also,an available vector 562 may be a sensing vector that indicates ambiguityin its analysis. The method then continues at 564, and determineswhether all available sensing vectors have been analyzed. If so, themethod continues to step 566, where the best vector is selected. Step566 may include sub-methods to resolve ambiguities, if present, in theavailable or unsuitable vectors 562, 570. The method then ends at 560.

If not all sensing vectors have been considered when at step 564, themethod continues by considering a different sensing vector, as indicatedat 568. The method then returns to step 550 where a new detectionthreshold is selected for the “next” sensing vector.

Referring still to FIG. 12, in one illustrative example, a singlesensing vector is available, due, for example, to limitations on theimplanted device (i.e. only two electrodes are available) or due to adevice failure (one or more electrodes may have a faulty connection).If, at step 566, a vector that has been determined to be unsuitable at556 and 570 is selected, a flag may be set indicating that an errorindicating poor sensing vector is to be annunciated to the programmeror, if the method is performed by the programmer itself, that the useror physician is to be notified.

The present invention includes certain embodiments in which the abovemethods may be performed by the implantable device in response todetected conditions, a request from an associated programmer, atintervals, or for other suitable reasons. Detected conditions promptingperformance of vector analysis may include the occurrence of repeateddifficulty with sensing, for example, the identification of aninordinate amount of double detections or a failure to consistentlydetect events. Another detected condition may be a rise in SNR or a dropin detected amplitude either below a predetermined level or to a levelthat creates sensing difficulties (for example, the range of 1.7millivolts to 2.0 millivolts in a tiered sensor having 2.0 millivolt and4.0 millivolt selectable dynamic sensing ranges).

These methods may be performed by an implantable cardiac stimulus devicehaving a housing containing operational circuitry, or multiple housingstethered together containing operational circuitry distributed among thehousings. The operational circuitry may be adapted to perform various ofthe above steps and methods using either or both of the analog and/ordigital domain using appropriate components, devices, and connections,including but not limited to a microcontroller and associated memory.

In an illustrative embodiment in which one or more of the above methodsare performed by an implantable medical device system, if it isdetermined that user input is needed to determine whether an identifiedLSPS corresponds to a score or a possible score, the method may includefurther steps. In particular, after the LSPS is identified, it may bedetermined whether a programmer is currently in communication with theimplantable medical device system. If so, then telemetrycircuitry/devices are used to contact the programmer to request the userinput. Otherwise, the implantable medical device system sets aside theLSPS for later verification once a programmer is available forcommunication allowing the user input. If more than one LSPS is largerthan the largest available Score, information indicating the successivenext LSPS (or several LSPS's) may be stored until communication with aprogrammer is available.

Further, the present invention includes embodiments in which at leastcertain steps of the above methods may be performed by a programmeradapted for use with an implantable medical device, the programmer beingadapted to communicate (for such embodiments, communication ispreferably but not necessarily wireless) with an implantable medicaldevice. The programmer may comprise various appropriate components andcircuitry for performing method steps. The programmer may directoperation of the implantable medical device to perform the method(s), orthe programmer may use the implantable medical device to capture datafrom the patient and transfer the captured data to the programmeritself. In some embodiments, certain method steps (event detection, forexample) may be performed by the implantable medical device while othersteps (detected event analysis, for example) may be performed by theassociated programmer.

The present invention also includes embodiments in which machinereadable media encodes an instruction set or sets for performing theabove methods using operational circuitry of an implantable medicaldevice or, in some embodiments, using circuitry in a programmer for usein association with an implantable medical device.

An illustrative embodiment includes a method involving an implantablemedical system adapted to define a plurality of sensing vectors betweenelectrodes implanted in a patient, and a programmer adapted forcommunication with the implantable medical device. The method maycomprise the implantable medical system capturing cardiac signal datausing at least one of the plurality of sensing vectors. Further, themethod may include analyzing data related to the captured cardiac signaldata and either determining that an identified sensing vector issuitable for cardiac event detection; or determining that one or moresensing vectors is to be analyzed.

The method may, if it is determined that one or more sensing vectors isto be analyzed, further comprise the implantable medical systemcapturing additional cardiac signal data using one or more other sensingvectors. Then, the method may also include analyzing data related to thecaptured additional cardiac signal data and: determining that anidentified sensing vector is suitable for cardiac event detection;determining that there is a best available sensing vector; or using theprogrammer to request operator input to complete a sensing vectorselection process.

In an illustrative embodiment of the above method, the analyzing anddetermining steps are performed by the programmer, and the method alsocomprises the implantable medical system transmitting data to theprogrammer for performing the analyzing and determining steps.Alternatively, the analyzing and determining steps are performed by theimplantable medical system. If this is the case, the method may be suchthat the implantable medical system performs the capturing, analyzingand determining steps periodically and/or occasionally. In anotherembodiment, the implantable medical system performs the capturing,analyzing and determining steps in response to a request from theprogrammer. In some embodiments, the implantable medical system includessignal processing circuitry having at least a first dynamic range and asecond dynamic range and, if the identified sensing vector is suitablefor cardiac event detection, a dynamic range is selected.

Another illustrative embodiment includes a programmer for use with animplantable medical device system, the implantable medical device systemincluding electrodes for sensing cardiac signals, the programmercomprising telemetry circuitry for communicating with the implantablemedical device system, a user interface for communicating with anoperator, and operational circuitry configured to perform a method ofselecting a sensing vector for the implantable medical device system.The method of selecting a sensing vector may comprise a) directing theimplantable medical device system to capture and transmit data relatedto a selected sensing vector; b) analyzing the transmitted data todetermine if the selected sensing vector is well-suited for cardiacevent detection; if the selected sensing vector is well suited forcardiac event detection, directing the implantable medical device systemto use the selected sensing vector for cardiac event detection; orrepeating steps a) and b) with another sensing vector.

The programmer may be such that the operational circuitry is furtherconfigured to perform the steps of, if a second sensing vector is wellsuited for cardiac event detection, directing the implantable medicaldevice system to use the second sensing vector for cardiac eventdetection; or repeating steps a) and b) with a yet another sensingvector; if a third sensing vector is well suited for cardiac eventdetection, directing the implantable medical device system to use thethird sensing vector for cardiac event detection; or x) identifying thebest of the sensing vectors and directing the implantable medical devicesystem to use the best sensing vector for cardiac event detection. Theoperational circuitry may be further configured to perform the steps ofidentifying an appropriate dynamic range for the implantable medicaldevice system and directing the implantable medical device system to usethe identified dynamic range. The operational circuitry may be adaptedsuch that steps a) and b) allow for determination of at least an actualscore or multiple possible scores, the multiple possible scores beingdetermined when analysis reveals a likely ambiguity, each possible scorecorresponding to an outcome of the ambiguity. Step x) may includeidentifying a set of available scores including any scores and possiblescores determined when steps b) were performed, y) selecting a bestavailable score from the set of available scores; and, if the bestavailable score is an actual score, identifying a corresponding sensingvector as the best of the sensing vectors, if the best available scoreis a possible score, requesting user input to eliminate the likelyambiguity, determining whether the user input verifies an outcomecorresponding to the possible score and, if so, identifying acorresponding sensing vector as the best of the sensing vectors, or, ifnot, removing the possible score from the set of available scores andreturning to step y).

In another embodiment, the operational circuitry is adapted such thatsteps a) and b) also allow for a determination that a vector isunsuitable for cardiac event detection, and, if a particular vector isdetermined to be unsuitable for cardiac event detection, that vector isnot considered in step x). The operational circuitry may be adapted suchthat steps a) and b) include calculating either a score or, if ambiguityis likely, multiple possible scores for the selected sensing vector andthe selected sensing vector is well-suited for cardiac event detectionif a score is calculated and the score exceeds a threshold for theselected sensing vector. The operational circuitry may be adapted suchthat, if step b) is repeated for multiple sensing vectors, the thresholdis adapted to each of the sensing vectors. The operational circuitry maycomprise readable memory encoding an instruction set for performing themethod of selecting a sensing vector.

An illustrative embodiment includes an implantable medical device systemincluding electrodes for sensing cardiac signals and operationalcircuitry coupled to the electrodes, the electrodes defining a pluralityof sensing vectors for observing electrical activity of a patient'sheart, the operational circuitry configured to perform a method ofselecting a sensing vector for the implantable medical device system.The method may comprise a) capturing data related to a selected sensingvector; b) analyzing the captured data to determine if the selectedsensing vector is well-suited for cardiac event detection; if theselected sensing vector is well suited for cardiac event detection,using the selected sensing vector for cardiac event detection; orrepeating steps a) and b) with another sensing vector. The operationalcircuitry may be further configured to perform the steps of, if theanother sensing vector is well suited for cardiac event detection, usingthe second sensing vector for cardiac event detection; or repeatingsteps a) and b) with a yet another sensing vector; if the yet anothersensing vector is well suited for cardiac event detection, using the yetanother sensing vector for cardiac event detection; or x) identifyingthe best of the sensing vectors and using the best sensing vector forcardiac event detection. The implantable medical device system mayfurther comprise telemetry circuitry for communicating with a programmerhaving a user interface, wherein the operational circuitry is adaptedsuch that steps a) and b) allow for determination of at least an actualscore or multiple possible scores, the multiple possible scores beingdetermined when analysis reveals a likely ambiguity, each possible scorecorresponding to an outcome of the ambiguity; and step x) includes:identifying a set of available scores including any scores and possiblescores determined when steps a) and b) were performed; y) selecting abest available score from the set of available scores and: if the bestavailable score is an actual score, identifying a corresponding sensingvector as the best of the sensing vectors; if the best available scoreis a possible score, using the telemetry circuitry to direct theprogrammer to request user input to eliminate the likely ambiguity,receiving a response from the programmer indicating the user input,determining whether the user input verifies an outcome corresponding tothe possible score and, if so, identifying a corresponding sensingvector as the best of the sensing vectors, or, if not, removing thepossible score from the set of available scores and returning to stepy).

The operational circuitry may be adapted such that steps a) and b) alsoallow for a determination that a vector is unsuitable for cardiac eventdetection, and, if a particular vector is determined to be unsuitablefor cardiac event detection, that vector is not considered in step x).In another embodiment, the operational circuitry is adapted such thatstep b) includes calculating either a score or, if ambiguity is likely,multiple possible scores for the selected sensing vector and theselected sensing vector is well-suited for cardiac event detection if ascore is calculated and the score exceeds a threshold for the selectedsensing vector. The operational circuitry may be adapted such that, ifstep b) is repeated for multiple sensing vectors, the threshold isadapted to each of the sensing vectors. The operational circuitry maycomprise readable memory encoding an instruction set for performing themethod of selecting a sensing vector.

Another illustrative embodiment includes a method of cardiac signalanalysis in an implantable cardiac stimulus system having at least firstand second sensing electrodes defining a first sensing vectortherebetween. The method may comprise selecting a detection threshold,capturing a plurality of detected events in which an electrical signalsensed along the first sensing vector exceeds the detection threshold,analyzing at least one metric related to a signal to noise ratio andamplitude for the plurality of detected events, determining whether thefirst sensing vector is suitable for cardiac event detection, unsuitablefor cardiac event detection, or available for cardiac event detection.

Another illustrative embodiment is a method of directing operation of animplantable cardiac stimulus system comprising an implantable devicehaving operational circuitry coupled to a plurality of sensingelectrodes disposed within a patient and defining a plurality of sensingvectors for performing cardiac event detection, the system furthercomprising a programmer adapted for communication with the implantabledevice. The method may comprise the programmer directing data capture bythe implantable device using at least one of the plurality of sensingvectors; and the programmer analyzing at least one of the plurality ofsensing vectors and: determining that an identified sensing vector issuitable for cardiac event detection; or, determining that operatorinput is needed to complete a sensing vector selection process. The stepof determining that operator input is needed to complete a sensingvector selection process may be used when ambiguity arises in theanalyzing step. The operator input may be an indication of whether aT-wave component or a QRS-complex component of a cardiac signal, eachcaptured using the same sensing vector, has a greater amplitude. Theoperator input may be an indication of whether a desired cardiaccomponent of cardiac signal or a noise artifact, each using captured thesame sensing vector, has a greater amplitude. The method may furtherinclude, if none of a set of at least two sensing vectors is determinedto be suitable for cardiac event detection, the method includesrequesting operator input using the programmer.

In another embodiment, the step of analyzing at least one of a pluralityof the sensing vectors includes calculating a score related to thequality of detection available for a sensing vector, and the step ofdetermining that an identified sensing vector is suitable for cardiacevent detection includes comparing the score for the selected sensingvector to a threshold. The method may be such that the step of analyzingat least one of a plurality of the sensing vectors includes calculatinga score related to the quality of detection available for a sensingvector, and the step of determining that an identified sensing vector issuitable for cardiac event detection includes selecting the sensingvector having the highest score. The step of analyzing at least one of aplurality of the sensing vectors may include attempting to calculate ascore related to the quality of detection available for at least two ofthe sensing vectors, failing to calculate the score for at least onesensing vector due to uncertainty, establishing possible outcomes forthe score given possible resolutions of the uncertainty, and setting aflag for the at least one sensing vector for which the score was notcalculated. The method may be performed such that the step ofdetermining that an identified sensing vector is suitable for cardiacevent detection includes determining that a calculated score exceeds apredetermined threshold and selecting a corresponding sensing vector, ordetermining that a calculated score exceeds all other scores andpossible outcomes and selecting a corresponding sensing vector; and thestep of determining that operator input is needed includes determiningthat a possible outcome exceeds all other possible outcomes andcalculated scores.

In one embodiment, the programmer may direct the implantable device tocapture data and perform one or more steps of amplifying, filtering,and/or digitizing the captured data. In another embodiment, theimplantable device is adapted to capture detections by comparison of asignal sensed using a sensing vector to a threshold, the programmerdirects the implantable device to capture a set of detections using asensing vector, and the programmer directs the implantable device tosend data related to the set of detections to the programmer for use inthe step of analyzing at least one of the plurality of sensing vectors.

Another illustrative embodiment includes a method of directing operationof an implantable cardiac stimulus system comprising an implantabledevice having operational circuitry coupled to a plurality of sensingelectrodes disposed within a patient and defining a plurality of sensingvectors for performing cardiac event detection, the system furthercomprising a programmer adapted for communication with the implantabledevice. The method may comprise the programmer directing the implantabledevice to capture first data using a first sensing vector, theprogrammer directing the implantable device to transmit second datarelated to the captured first data, the programmer analyzing thetransmitted second data to determine whether the first sensing vector issuitable, within given threshold conditions, for use in cardiac eventdetection and analysis, and if so, selecting the first vector for use incardiac event detection and analysis; otherwise, the programmerdirecting the implantable device to capture and transmit additional datausing one or more additional sensing vectors. The step of the programmerdirecting the implantable device to capture and transmit additional datausing one or more additional sensing vectors may includes the programmerdirecting the implantable device to capture third data using a secondsensing vector, the programmer directing the implantable device totransmit fourth data related to the captured third data, the programmeranalyzing the transmitted fourth data to determine whether the secondsensing vector is suitable, within given threshold conditions, for usein cardiac event detection and analysis, and if so, selecting the secondcardiac vector for use in cardiac event detection and analysis,otherwise, the programmer directing the implantable device to captureand transmit additional data using at least a third sensing vector.

The step of the programmer directing the implantable device to captureand transmit additional data using one or more additional sensingvectors may include the programmer directing the implantable device tocapture fifth data using a third sensing vector, the programmerdirecting the implantable device to transmit sixth data related to thecaptured fifth data, the programmer analyzing the transmitted sixth datato determine whether the third sensing vector is suitable, within giventhreshold conditions, for use in cardiac event detection and analysisand, if so, selecting the third cardiac vector for use in cardiac eventdetection and analysis, otherwise, the programmer selecting a bestvector from among the first, second, and third sensing vectors for usein cardiac event detection and analysis. The step of the programmerdirecting the implantable device to capture and transmit additional datausing one or more additional sensing vectors may include the programmerdirecting the implantable device to capture third data using a secondsensing vector the programmer directing the implantable device totransmit fourth data related to the captured third data, the programmeranalyzing the transmitted fourth data to determine whether the secondsensing vector is suitable, within given threshold conditions, for usein cardiac event detection and analysis, and if so, selecting the secondcardiac vector for use in cardiac event detection and analysis,otherwise, the programmer selecting a best vector from among the firstand second sensing vectors for use in cardiac event detection andanalysis.

Another illustrative embodiment includes a method of operating animplantable cardiac stimulus system comprising an implantable devicehaving operational circuitry coupled to a plurality of sensingelectrodes disposed within a patient and defining a plurality of sensingvectors for performing cardiac event detection, the system furthercomprising a programmer adapted for communication with the implantabledevice. The method may comprise executing instructions with theprogrammer to analyze at least first and second sensing vectors definedbetween selected subsets of the plurality of sensing electrodes byinstructing the implantable device to perform data capture andtransmission related to the at least first and second sensing vectors,the instructions adapted to generate either a score related tocharacteristics of a signal sensed along a selected sensing vector, orat least two possible scores and an indication of uncertainty relativeto the possible scores; and, if no indications of uncertainty aregenerated, selecting whichever sensing vector has a highest score foruse in detecting cardiac events, or, if at least one indication ofuncertainty is generated: if a score exceeds other scores and allpossible scores, selecting a corresponding sensing vector for use indetecting cardiac events without resolving uncertainty related to atleast one possible score that does not exceed the identified score; andif an identified possible score exceeds all scores and other possiblescores, requesting input from an operator to settle the uncertaintyrelated to the possible score and, if the operator input resolves theuncertainty in favor of the identified possible score, selecting acorresponding sensing vector for use in detecting cardiac events.

The step of requesting input from an operator may include asking theoperator to determine whether the peak amplitude of a sensed QRS complexis greater than the peak amplitude of a sensed T-wave. Also, the step ofrequesting input from an operator may include asking the operator todetermine whether the peak amplitude of a sensed QRS complex is greaterthan the peak amplitude of a sensed noise signal. Further, the step ofrequesting input from an operator includes asking the operator todetermine whether a highest peak in a sensed signal is an R-wave peak.

Another illustrative embodiment includes a method of operating animplantable cardiac stimulus system comprising an implantable devicehaving operational circuitry to coupled to a plurality of sensingelectrodes disposed within a patient and defining a plurality of sensingvectors for performing cardiac event detection, the system furthercomprising a programmer adapted for communication with the implantabledevice. The method may comprise executing vectoring instructions withthe programmer to analyze a first sensing vector defined between aselected subset of the plurality of sensing electrodes by at leastinstructing the implantable device to perform data capture andtransmission related to the first sensing vector, wherein the vectoringinstructions are adapted to generate either a score related tocharacteristics of a signal sensed along a selected sensing vector, orat least two possible scores and an indication of uncertainty relativeto the possible scores; if the analysis of the first sensing vectorgenerates a first score, comparing the first score to a first thresholdand, if the first score exceeds the first threshold, selecting the firstsensing vector for use in detecting cardiac events; otherwise, executingthe vectoring instructions with the programmer to analyze a secondsensing vector defined between another selected subset of the pluralityof sensing electrodes by at least instructing the implantable device toperform data capture and transmission related to the second sensingvector; and if the analysis of the second sensing vector generates asecond score, comparing the second score to a second threshold and, ifthe second score exceeds the second threshold, selecting the secondsensing vector for use in detecting cardiac events.

The method may be such that the second sensing vector is not analyzed ifthe first score exceeds the first threshold. The method may furthercomprise, if the first score does not exceed the first threshold or afirst score is not generated, and the second score does not exceed thesecond threshold or a second score is not generated; then, executing thevectoring instructions with the programmer to analyze a third sensingvector defined between yet another selected subset of the plurality ofsensing electrodes by at least instructing the implantable device toperform data capture and transmission related to the third sensingvector; and if the analysis of the third sensing vector generates athird score, comparing the third score to a third threshold and, if thethird score exceeds the third threshold, selecting the third sensingvector for use in detecting cardiac events.

In another method, if none of the first, second or third thresholds areexceeded, the method further comprises starting with a set of scoresand/or possible scores generated by executing the vectoringinstructions: a) identifying a greatest available score from the scoresand/or possible scores; b) if the greatest available score is a score,selecting sensing vector corresponding to the score for use in detectingcardiac events; c) if a greatest available score is a possible score,requesting input from an operator to determine whether the identifiedpossible score should be treated as an actual score or discarded; d) ifthe operator input indicates that the identified possible score shouldbe treated as an actual score, selecting a sensing vector correspondingto the identified possible score for use in detecting cardiac events; e)if the operator input indicates that the identified possible scoreshould be discarded, removing the identified possible score from the setof scores and/or possible scores, treating an associated possible scoreas a score, and returning to step a). The method may be such that, iffirst and second scores are generated by executing the vectoringinstructions on the first and second sensing vectors and neither scoreexceeds a corresponding threshold, the method further comprisesdetermining whether the greater of the first and second scores exceeds athird threshold and, if so, selecting the greater of the first andsecond scores for use in detecting cardiac events.

The scores and possible scores may be generated by calculating asignal-to-noise ratio and observing a peak amplitude for a selectedsensing vector. The scores and possible scores may also be generated byinserting the signal-to-noise ratio and observed peak amplitude into aformula. Instead, the scores and possible scores may be generated byinserting the signal-to-noise ratio and observed peak amplitude into alook-up table.

Another illustrative embodiment includes a method of operating animplantable cardiac stimulus system comprising an implantable devicehaving operational circuitry coupled to a plurality of sensingelectrodes disposed within a patient and defining a plurality of sensingvectors for performing cardiac event detection, the system furthercomprising a programmer adapted for communication with the implantabledevice. The method may comprise the programmer instructing theimplantable device to perform at least data capture and transmissionrelative to a first sensing vector, the programmer analyzing transmitteddata related to the first sensing vector and returning one of: a) ascore indicating the quality of a signal captured along the firstsensing vector; b) at least two possible scores indicating the qualityof the signal captured along the first sensing vector wherein operatorinput is needed to determine which possible score is correct; or c) anindication that the sensing vector under review is unsuitable forcardiac signal sensing; the programmer determining whether the firstsensing vector receives a score indicating that the first sensing vectoris well suited to cardiac signal detection and, if not, the programmerinstructing the implantable device to perform at least data capture andtransmission relative to a second sensing vector; and the programmeranalyzing transmitted data related to the second sensing vector insimilar fashion to the first sensing vector. The method may furthercomprise the programmer determining whether the second sensing vectorreceives a score indicating that the second sensing vector is wellsuited to cardiac signal detection and, if not, the programmeridentifying which of the returned scores or possible scores is highestand, if a possible score is highest, the programmer querying an operatorfor the device to determine whether the highest possible score iscorrect; if so, a corresponding sensing vector is selected for use indetecting cardiac activity; else, the programmer repeats the step ofselecting which of the returned scores or possible scores is highestuntil a sensing vector is selected.

Another illustrative embodiment includes a method of operating animplantable cardiac stimulus system comprising operational circuitrycoupled to a plurality of sensing electrodes disposed within a patientand defining a plurality of sensing vectors for performing cardiac eventdetection. The method may comprise the operational circuitry analyzingat least one of the plurality of sensing vectors; and the operationalcircuitry either: determining that an identified sensing vector issuitable for cardiac event detection; or determining that operator inputis needed to complete a sensing vector selection process. The step ofdetermining that operator input is needed to complete a sensing vectorselection process may be a step of last resort used when the operationalcircuitry cannot resolve or eliminate ambiguity in the analyzing step.The operator input may be an indication of whether a T-wave component ora QRS-complex component of a cardiac signal, each captured using thesame sensing vector, has a greater amplitude. The operator input may bean indication of whether a desired cardiac component of cardiac signalor a noise artifact, each using captured the same sensing vector, has agreater amplitude.

The method may be such that the step of determining that operator inputis needed is performed only after all of the sensing vectors have beenanalyzed. In another method, the step of analyzing at least one of aplurality of the sensing vectors includes calculating a score related tothe quality of detection available for a sensing vector; and the step ofdetermining that an identified sensing vector is suitable for cardiacevent detection includes comparing the score for the selected sensingvector to a threshold. In yet another method, the step of analyzing atleast one of a plurality of the sensing vectors includes calculating ascore related to the quality of detection available for a sensingvector; and the step of determining that an identified sensing vector issuitable for cardiac event detection includes selecting the sensingvector having the highest score. The step of analyzing at least one of aplurality of the sensing vectors may include attempting to calculate ascore related to the quality of detection available for at least two ofthe sensing vectors, failing to calculate the score for at least onesensing vector due to uncertainty, establishing possible outcomes forthe score given possible resolutions of the uncertainty, and setting aflag for the at least one sensing vector for which the score was notcalculated. The method may also be such that the step of determiningthat an identified sensing vector is suitable for cardiac eventdetection includes determining that a calculated score exceeds apredetermined threshold and selecting a corresponding sensing vector; ordetermining that a calculated score exceeds all other scores andpossible outcomes and selecting a corresponding sensing vector; and thestep of determining that operator input is needed includes determiningthat a possible outcome exceeds all other possible outcomes andcalculated scores.

Another illustrative embodiment includes a method of operating animplantable cardiac stimulus system comprising operational circuitrycoupled to a plurality of sensing electrodes disposed within a patientand defining a plurality of sensing vectors for performing cardiac eventdetection. The method may comprise analyzing a first sensing vector todetermine whether it is suitable, within given threshold conditions, foruse in cardiac event detection and analysis, and if so, selecting thefirst vector for use in cardiac event detection and analysis, otherwise,analyzing one or more additional sensing vectors. The step of analyzingone or more additional vectors may include analyzing a second sensingvector to determine whether it is suitable, within given thresholdconditions, for use in cardiac event detection and analysis, and if so,selecting the second cardiac vector for use in cardiac event detectionand analysis; and, otherwise, analyzing at least a third sensing vector.

The step of analyzing at least a third sensing vector may includedetermining whether the third sensing vector is suitable, within giventhreshold conditions, for use in cardiac event detection and analysisand, if so, selecting the third cardiac vector for use in cardiac eventdetection and analysis; and, otherwise, selecting a best vector fromamong the first, second, and third sensing vectors for use in cardiacevent detection and analysis. The step of analyzing one or moreadditional vectors may include analyzing a second sensing vector todetermine whether it is suitable, within given threshold conditions, foruse in cardiac event detection and analysis; and, if so, selecting thesecond cardiac vector for use in cardiac event detection and analysis;else, selecting a best vector from among the first and second sensingvectors for use in cardiac event detection and analysis.

Another illustrative embodiment includes a method of operating animplantable cardiac stimulus system comprising a controller coupled to aplurality of sensing electrodes adapted for disposition in a patient.The method may comprise executing instructions with the controller toanalyze at least first and second sensing vectors defined betweenselected subsets of the plurality of sensing electrodes, theinstructions adapted to generate either a score related tocharacteristics of a signal sensed along a selected sensing vector, orat least two possible scores and an indication of uncertainty relativeto the possible scores; and, if no indications of uncertainty aregenerated, selecting whichever sensing vector has a highest score foruse in detecting cardiac events. If at least one indication ofuncertainty is generated, and if a score exceeds other scores and allpossible scores, the method may include selecting a correspondingsensing vector for use in detecting cardiac events without resolvinguncertainty related to at least one possible score that does not exceedthe identified score; or if an identified possible score exceeds allscores and other possible scores, the method may include requestinginput from an operator to settle the uncertainty related to the possiblescore and, if the operator input resolves the uncertainty in favor ofthe identified possible score, selecting a corresponding sensing vectorfor use in detecting cardiac events.

The step of requesting input from an operator may include asking theoperator to determine whether the peak amplitude of a sensed QRS complexis greater than the peak amplitude of a sensed T-wave. The step ofrequesting input from an operator may include asking the operator todetermine whether the peak amplitude of a sensed QRS complex is greaterthan the peak amplitude of a sensed noise signal. The step of requestinginput from an operator may include asking the operator to determinewhether a highest peak in a sensed signal is an R-wave peak.

Another illustrative embodiment includes a method of operating animplantable cardiac stimulus system comprising a controller coupled to aplurality of sensing electrodes adapted for disposition in a patient.The method may comprise executing vectoring instructions with thecontroller to analyze a first sensing vector defined between a selectedsubset of the plurality of sensing electrodes, wherein the vectoringinstructions are adapted to generate either a score related tocharacteristics of a signal sensed along a selected sensing vector, orat least two possible scores and an indication of uncertainty relativeto the possible scores; if the analysis of the first sensing vectorgenerates a first score, comparing the first score to a first thresholdand, if the first score exceeds the first threshold, selecting the firstsensing vector for use in detecting cardiac events; otherwise, executingthe vectoring instructions with the controller to analyze a secondsensing vector defined between another selected subset of the pluralityof sensing electrodes; and if the analysis of the second sensing vectorgenerates a second score, comparing the second score to a secondthreshold and, if the second score exceeds the second threshold,selecting the second sensing vector for use in detecting cardiac events.The method may be such that the second sensing vector is not analyzed ifthe first score exceeds the first threshold.

If the first score does not exceed the first threshold or a first scoreis not generated, and the second score does not exceed the secondthreshold or a second score is not generated, then the method may alsoinclude executing the vectoring instructions with the controller toanalyze a third sensing vector defined between yet another selectedsubset of the plurality of sensing electrodes, and if the analysis ofthe third sensing vector generates a third score, comparing the thirdscore to a third threshold and, if the third score exceeds the thirdthreshold, selecting the third sensing vector for use in detectingcardiac events. If none of the first, second or third thresholds areexceeded, the method may further comprise starting with a set of scoresand/or possible scores generated by executing the vectoring instructionsand: a) identifying a greatest available score from the scores and/orpossible scores; b) if the greatest available score is a score,selecting sensing vector corresponding to the score for use in detectingcardiac events; c) if a greatest available score is a possible score,requesting input from an operator to determine whether the identifiedpossible score should be treated as an actual score or discarded; d) ifthe operator input indicates that the identified possible score shouldbe treated as an actual score, selecting a sensing vector correspondingto the identified possible score for use in detecting cardiac events; e)if the operator input indicates that the identified possible scoreshould be discarded, removing the identified possible score from the setof scores and/or possible scores, treating an associated possible scoreas a score, and returning to step a).

If first and second scores are generated by executing the vectoringinstructions on the first and second sensing vectors and neither scoreexceeds a corresponding threshold, the method may include determiningwhether the greater of the first and second scores exceeds a thirdthreshold and, if so, selecting the greater of the first and secondscores for use in detecting cardiac events. The method may be such thatthe scores and possible scores are generated by calculating asignal-to-noise ratio and observing a peak amplitude for a selectedsensing vector. Also, the scores and possible scores may be generated byinserting the signal-to-noise ratio and observed peak amplitude into aformula. The scores and possible scores may also be generated byinserting the signal-to-noise ratio and observed peak amplitude into alook-up table.

Another illustrative embodiment includes a method of cardiac signalanalysis in an implantable cardiac stimulus system having a plurality ofsensing electrodes and operational circuitry coupled thereto. The methodmay comprise the operational circuitry executing vectoring instructionsrelative to a first sensing vector, the vectoring instructions causingthe operational circuitry to return one of: a) a score indicating thequality of a signal captured along the first sensing vector; b) at leasttwo possible scores indicating the quality of the signal captured alongthe first sensing vector wherein operator input is needed to determinewhich possible score is correct; or c) an indication that the sensingvector under review is unsuitable for cardiac signal sensing. The methodmay also include the operational circuitry determining whether the firstsensing vector receives a score indicating that the first sensing vectoris well suited to cardiac signal detection and, if not, the operationalcircuitry executing the vectoring instructions relative to a secondsensing vector. The method may further comprise the operationalcircuitry determining whether the second sensing vector receives a scoreindicating that the second sensing vector is well suited to cardiacsignal detection and, if not, the operational circuitry selecting whichof the returned scores or possible scores is highest and, if a possiblescore is highest, the operational circuitry querying an operator for thedevice to determine whether the highest possible score is correct; ifso, a corresponding sensing vector is selected for use in detectingcardiac activity; else, the operational circuitry repeats the step ofselecting which of the returned scores or possible scores is highestuntil a sensing vector is selected.

An illustrative embodiment includes a method of cardiac signal analysiscomprising analyzing data captured along one or more of a plurality ofsensing vectors defined between implanted electrodes and selecting oneof the plurality of sensing vectors for primary use in cardiac eventdetection. The step of analyzing data captured along one of theplurality of sensing vectors may include identifying a number ofdetected events by comparison of a received signal to a detectionthreshold, characterizing, by analysis of intervals between the detectedevents, the detected events as: a) QRS events; b) artifacts; or c)unidentifiable; and, if sufficient detected events are QRS events,calculating a signal-to-noise ratio and amplitude associated with thesensing vector; otherwise parsing, by analysis of event intervals andamplitudes, the unidentifiable events into: a) QRS events; b) artifacts;or c) unparseable. At this point, if sufficient detected events are nowQRS events, the method includes calculating a signal-to-noise ratio andamplitude associated with the sensing vector. The method may beperformed by operational circuitry of an implanted medical device. Thestep of identifying a number of detected events may be performed by animplantable medical device, and the other steps are performed by aprogrammer adapted to communicate with the implantable medical device.In yet another method, at least one step is performed by an implantablemedical device and at least one other step is performed by a programmeradapted to communicate with the implantable medical device.

Devices, including implantable medical devices and programmers, that areadapted to perform one or more steps of the above methods, as well assystems comprising implantable medical devices and programmers that areadapted as systems to perform any of these methods and/or steps, arealso included in illustrative embodiments.

Those skilled in the art will recognize that the present invention maybe manifested in a variety of forms other than the specific embodimentsdescribed and contemplated herein. Accordingly, departures in form anddetail may be made without departing from the scope and spirit of thepresent invention as described in the appended claims.

What is claimed is:
 1. A medical device comprising an implantablestimulus device including an implantable lead and operational circuitrycontained within a housing, the operational circuitry coupled to aplurality of electrodes for sensing cardiac activity, wherein theplurality of electrodes includes at least one electrode on the housingand at least one electrode on the lead; the operational circuitry beingconfigured to perform the following: receive a signal from theelectrodes; sense a plurality of detected events from the signalreceived from the electrodes, the detected events separated byintervals; analyze consecutive intervals defined between pairs ofdetected events; determine that at least two consecutive intervals areequal within a predefined margin; determine that each of the at leasttwo equal consecutive intervals are shorter than a predefined duration;and after determining the consecutive intervals are equal within thepredefined margin and shorter than the predefined duration, markwhichever of the two detected events occurring at the start of each ofthe consecutive intervals is of lesser amplitude as noise and the otherof the two detected events as QRS; and wherein the operational circuitryis configured to sense the plurality of detected events by: comparing asensing threshold set to a selected amplitude to the received signalfrom the electrodes; observing crossing of the sensing threshold anddeclaring a detected event; applying a refractory period forpredetermined period of time; and again comparing the sensing thresholdset to the selected amplitude to the received signal from the electrodesafter the refractory period to sense a subsequent detected event.
 2. Themedical device of claim 1 wherein the plurality of electrodes define aplurality of sensing vectors and the operational circuitry is configuredto perform vector selection to select a default vector for use insensing cardiac activity, in which the operational circuitry isconfigured to analyze said detected events marked as QRS to determine anamplitude factor used for vector selection.
 3. The medical device ofclaim 2 wherein the operational circuitry is configured to analyze saiddetected events marked as noise to determine a noise factor used forvector selection.
 4. The medical device of claim 1 wherein the pluralityof electrodes define a plurality of sensing vectors and the operationalcircuitry is configured to perform vector selection to select a defaultvector for use in sensing cardiac activity, in which the operationalcircuitry is configured to analyze detected events marked as noise todetermine a noise factor used for vector selection.
 5. The medicaldevice of claim 1 wherein the operational circuitry is configured to setthe selected amplitude in a setting process by: the operationalcircuitry setting an initial sensing floor; the operational circuitrycomparing the initial sensing floor to the received signal until thereceived signal crosses the initial sensing floor; the operationalcircuitry raising the sensing floor until a timeout occurs; and theoperational circuitry setting the selected amplitude relative a level ofthe sensing floor at which the timeout occurs.
 6. A medical device as inclaim 1 wherein the implantable cardiac stimulus device is configured asa subcutaneous-only implantable defibrillator such that all electrodesare disposed outside of the ribcage of the patient.
 7. A medical deviceas in claim 1 wherein the implantable cardiac stimulus device isconfigured as a transvenous implantable defibrillator such that the leadis configured to enter the patient's venous system and attach to theheart thereof.
 8. A medical device as in claim 1 wherein the housing hasat least two electrodes disposed thereon.
 9. A medical device as inclaim 1, wherein the operational circuitry is configured such that thepredefined margin calls for the duration of the at least two consecutiveintervals to be within a set time period of one another.
 10. A medicaldevice as in claim 9 wherein the set time period is 50 milliseconds. 11.A method of operation in a medical device comprising a housing, animplantable lead, a plurality of electrodes and operational circuitrydisposed within the housing, the operational circuitry coupled to theplurality of electrodes for sensing cardiac activity, the plurality ofelectrodes includes at least one electrode on the housing and at leastone electrode on the lead, the method comprising the operationalcircuitry: receiving a signal from the electrodes; sensing a pluralityof detected events from the signal received from the electrodes, thedetected events separated by intervals; analyzing consecutive intervalsdefined between pairs of detected events; determining that at least twoconsecutive intervals are equal, within a predefined margin; determiningthat the at least two equal consecutive intervals are each shorter thana predefined duration; after determining the consecutive intervals areequal within the predefined margin and shorter than the predefinedduration, marking whichever of the two detected events occurring at thestart of each of the consecutive intervals is of lesser amplitude asnoise and the other of the two detected events as QRS; and using the QRSto identify and select a default sensing vector for the medical deviceand using the default sensing vector to sense cardiac activity of apatient; wherein the operational circuitry is configured to sense theplurality of detected events by: comparing a sensing threshold set to aselected amplitude to the received signal from the electrodes; observingcrossing of the sensing threshold and declaring a detected event;applying a refractory period for predetermined period of time; and againcomparing the sensing threshold set to the selected amplitude to thereceived signal from the electrodes after the refractory period to sensea subsequent detected event.
 12. A method of vector selection in amedical device having a plurality of electrodes that define a pluralityof sensing vectors and operational circuitry coupled to the plurality ofelectrodes, the method comprising: performing the method of claim 11;and analyzing said detected events marked as QRS to determine anamplitude factor used for vector selection.
 13. A method of vectorselection as in claim 12, further comprising analyzing said detectedevents marked as noise to determine a noise factor used for vectorselection.
 14. A method of vector selection in a medical device having aplurality of electrodes that define a plurality of sensing vectors andoperational circuitry coupled to the plurality of electrodes, the methodcomprising: performing the method of claim 11; and analyzing detectedevents marked as noise to determine a noise factor used for vectorselection.
 15. A method as in claim 11 further comprising theoperational circuitry setting the selected amplitude by: setting aninitial sensing floor; comparing the initial sensing floor to thereceived signal until the received signal crosses the initial sensingfloor; raising the sensing floor until a timeout occurs; and setting theselected amplitude relative to a level of the sensing floor at which thetimeout occurs.
 16. A method as in claim 11 wherein the medical deviceis a subcutaneous-only implantable defibrillator, and the operationalcircuitry comprises a charging sub-circuit and a power storagesub-circuit for building up a stored voltage for cardiac stimulus takingthe form of defibrillation therapy, and the method further comprises theoperational circuitry using the selected sensing vector to identify atreatable arrhythmia and the operational circuitry delivering adefibrillation therapy, and the step of receiving a signal from theelectrodes is performed using electrodes placed outside of the ribcageof a patient.
 17. A method as in claim 11 wherein the medical device isa transvenous defibrillator and the implantable lead is configured to beplaced inside of the heart of a patient, and the operational circuitrycomprises a charging sub-circuit and a power storage sub-circuit forbuilding up a stored voltage for cardiac stimulus taking the form ofdefibrillation therapy, and the method further comprises the operationalcircuitry using the selected sensing vector to identify a treatablearrhythmia and the operational circuitry delivering a defibrillationtherapy, and the step of receiving a signal from the electrodes isperformed using one or more electrodes in or on the heart.
 18. A methodas in claim 11 wherein the housing has at least two electrodes disposedthereon.
 19. A method as in claim 11, wherein the operational circuitryis configured such that the predefined margin calls for the durations ofthe at least two consecutive intervals to be within a set time period ofone another.
 20. A method as in claim 19 wherein the set time period is50 milliseconds.